1) (m+1)(3-m)=3m-m^2+3-m=-m^2+2m+3
(5a-7b)(6b-a)=30ab-5a^2-42b^2+7ab= -5a^2-42b^2+37ab
(x^2-2y)(3x^2+y)+2y^2-3x^4=3x^4+x^2y-6x^2y-2y^2+2y^2-3x^4= -5x^2y
2) 4t(t-3)-t+3=4t(t-3)-(t-3)=(t-3)(4t-1)
mn-m+k-kn=m(n-1)+k(1-n)=m(n-1)-k(n-1)=(n-1)(m-k)
2x^2y+4xy-6-3x=2xy(x+2)-3(2+x)=(x+2)(2xy-3)